The use of Infrared Thermal Imagers, particularly for temperature measurement within an operating furnace environment, is reliant on the accurate evaluation of specific parameters, which the pyrometer requires in order to produce true temperature measurements.

The measurement of furnace tube temperatures presents specific problems which may detract from the precision of temperatures measurements. Images for temperature measurement within an operating furnace environment, are reliant upon the accurate evaluation of the target's emissivity and the reflected ambient radiation. Both parameters being manually entered into the pyrometer.

These parameters are an essential requirement if we are to achieve a true target temperature, but their exact values are quite impossible to determine. The following discussion is an attempt to qualify this statement.